Fe0.4Ta0.5P2O7-based composite membrane for high-temperature, low-humidity proton exchange membrane fuel cells

• Fe0.4Ta0.5P2O7 based composite membranes were prepared with a satisfactory mechanical strength.
• It showed high proton conductivity of 0.01 S cm−1 at 150 °C in an unhumidified condition.
• The membrane (t > 50 μm) has a gas-impermeability and low area-specific resistance (ASR).
• The ASR is 0.17 Ω cm2 at high temperature of 150 °C and low humidity of 6.6%RH.

An inorganic–organic composite membrane composed of Fe0.4Ta0.5P2O7 (FTPO) and sulfonated polystyrene-b-poly(ethylene/butylene)-b-polystyrene (sSEBS) is prepared and characterized. To gain satisfaction of both the proton conductivity and mechanical strength in composite membranes, the optimal content of sSEBS was determined to be 30 wt%, which resulted in high proton conductivities of approximately 0.01 S cm−1 between 50 and 150 °C even under an unhumidified condition, a tensile strength of 4.1 MPa, and an elongation at break of 613%. A homogeneous distribution of the FTPO particles in the matrix was achieved at the composite membrane thickness greater than 50 μm, providing gas-impermeability and low area-specific resistance (ASR) of the membrane (0.17 Ω cm2 at 150 °C and H2O vapor concentration of 30.8 vol%). Fuel cell tests using the composite membrane provided peak power densities of 265 and 303 mW cm−2 at 150 °C under an unhumidified condition and at a H2O vapor concentration of 30.8 vol%, respectively.